Structure sequence and possible superconductivity in potassium-doped fullerene C70Kx.

A sequence of doped fcc or doped rhombohedral, bct, bcc, and K-saturated fcc phases was observed in C 70 K x with increasing K concentration using x-ray-diffraction measurements. A model for the structure of the K-saturated fcc phase C 70 K 9 is proposed. Superconductivity in each phase was checked using ac magnetic-susceptibility measurements. A small diamagnetic transition was observed below 12 K in the doped rhombohedral phase. All other phases were nonsuperconducting down to 1.3 K